The Four Stroke Engine Cycle: How Stuff Works
The principle behind how the engine works is that if you put a little bit of high-energy fuel, such as gasoline, into a small, enclosed space and add a spark, a huge amount of energy will be released in the form of expanding gas. When a cycle of hundreds of these reactions happens every minute, this energy can be used to run a car. Currently, most cars on the market use the four-stroke combustion cycle (invented by Nikolaus Otto in 1867, so sometimes it's referred to as the Otto cycle). The four strokes in the Otto cycle are the intake stroke, the compression stoke, the combustion stroke and the exhaust stroke.